Piston and compressor structure



July 4, 1961 R. s. PETERSEN 2,99 ,00

PISTON AND COMPRESSOR STRUCTURE Filed Jan. 30, 1957 2 Sheets-Sheet 2DIES EL ENG/NE ROBERT s. PETERSEN,

INVENTOR.

HE'RZIG 8 JESSUP,

A T TORNE YS.

Unite States Patent 2,991,003 PISTON AND COMPRESSOR STRUCTURE Robert S.Petersen, 1236 S. Central Ave., Glendale 4, (I'alif. Filed Jan. 30,1957, Ser. No. 637,276 4 Claims. (Cl. 230-53) This invention relates tocompressors and more particularly to an improved gas compressor having anovel piston and cylinder assembly, and a control system in which aplurality of piston and cylinder assemblies may be operated with a highdegree of efiiciency in a multiple stage gas compressor.

In compressors in which gas is compressed at relatively high pressures,it is essential that the moving parts of the compressor system be sealedto minimize the escape of gas. As the pressure of the gas on which thecompressor operates is increased, the problem is magnified with theresult that in many compressors the degree of compression that can beachieved is limited by the eflfectiveness of the seals. In conventionalpiston and cylinder compressors, it is well known to mount one or morepiston rings on the piston which engages the cylinder wall to reduce theflow of gas past the piston. In general, if known types of pistonsealing rings are constructed of a soft enough material to provide aneffective seal, the piston rings rapidly become worn and lose theirefliciency. On the other hand, if the piston rings are constructed ofrelatively hard material to withstand wear, they generally do notprovide a good seal.

In multiple stage piston and cylinder compressors where several stagesare operated together synchronously,

the efiiciency of the over-all system is limited because the stroke ofeach of the pistons is a fixed distance, and with a given source ofpower the pumping efiiciency varies as a function of the pressure of thegas upon which the compressor is operating.

Accordingly, it is an object of the present invention to provide apiston and cylinder assembly including a new and improved seal betweenthe piston and the cylinder.

It is another object of the present invention to provide a new andimproved piston sealing ring having superior qualities of sealingefficiency and durability.

It is a further object of the present invention to provide a new andimproved multiple stage compressor.

It is still another object of the invention to provide an improvedmultiple stage compressor including superior piston and cylinder sealsalong with a novel compressor control system.

It is an additional object of the invention to provide an improvedmultiple stage compressor system including a novel compressor controlsystem.

Also among the objects of this invention is to provide improvements overthe prior art devices heretofore intended to accomplish similarpurposes.

It is additionally among the objects of this invention 'to provide in anew and improved piston construction,

new and improved, eflicient and highly eifective piston ringconstruction.

Another further object of the invention is the provision of a new andimproved piston ring construction in a piston of the character describedhaving maximum ability to withstand high pressures and achieving anoptimum sealing and wiping action.

Another object of the invention resides in the provision of new andimproved materials and structure thereof for obtaining optimumefficiency at minimum cost associated with ease of production andassembly or disassembly for renewal or replacement.

Yet another object of the invention is the provision of a new andimproved unique combination of materials adapted to obtain aself-lubricating piston action with optimum wiping characteristics andscaling properties in the combination illustrated, described andclaimed.

Yet another object of the invention is the provision of new and improvedring for retaining and installing or disassembling a piston of thedesired character described without modification of the basic pistonstructure but merely by the substitution, elimination or addition ofpiston ring members for varying the elfective piston ring area withoutaltering the over-all structure of the piston.

Yet another object of the invention is the provision in a piston of thecharacter described of new and improved means for removably inserting orreplacing any desired number of such piston ring members as hereindescribed.

Yet a further object of the invention is the provision of new andimproved ring members per se in a piston of the character described, orits like, which is continuous, self-lubricating and simple to replace orrepair.

Another further object of the invention is the provision of new andimproved ring expander means for use in connection with a piston ring ofthe preferred character described.

A further specific object of the invention is the provision ofreplaceablepiston construction and seat members therefor which arecapable of ready adjustment for establishing a desired degree of tensionagainst the cylinder wall.

Another object of the invention is the provision of new and improvedpiston means, including new and improved piston ring means adapted toscour and seat with utmost accuracy and elfectiveness against thecorresponding cylinder wall.

Other objects and purposes will appear from the following descriptionconsidered in the light of the accompanying drawings and claims.

In the drawings:

FIGURE 1 is a sectional view of a portion of a stage of a compressorincluding an illustrative embodiment of the improved piston and cylindersealing feature of the invention;

FIGURE 2 is an enlarged sectional view of a portion of the piston andcylinder arrangement of FIGURE 1;

FIGURE 3 is a perspective view of an expandable ring for use in theapparatus of FIGURES 1 and 2; and

FIGURE 4 is a circuit diagram of a multiple stage compressor including acontrol system in accordance with the invention.

By way of illustration but not of limitation, as a preferred embodimentof the invention, there is shown in the drawings a cylinder and pistonarrangement including a gas cylinder 1 and an hydraulic cylinder 2. Thegas cylinder 1 is enclosed at the right-hand end as by a cylinder head 3which is preferably threaded into the gas cylinder 1, wherein there ismounted, for reciprocation, a gas cylinder piston 4, linked to a pistonrod 5', preferably by means of a universal joint type or other preferredconnection comprising the members 6 and 7, which are fastener to thepiston rod 5 as by means of a cap screw 8.

Within the hydraulic cylinder 2 there is also mounted an hydraulicpiston 9 to which the piston rod 5 is connected as by means of athreaded stud, or the like 10. The end of the hydraulic cyliner 2adjacent the gas cylinder 1 is sealed by means of cap assembly 11 whichpreferably includes a supply line 12 through which hydraulic fluid isintroduced into the hydraulic cylinder 2 for movement of the hydraulicpiston 9. The gas cylinder 1 is attached to the cap assembly 11 by meansof a threaded cap ring 13. The piston rod 5 is slidably supported in thecap assembly 11, and an hydraulic fluid seal 14 surrounding the pistonrod 5 inhibits the flow of hydraulic fluid along the surface of thepiston rod 5.

The apparatus of FIGURE 1 illustrates an hydraulic fluid piston 9 whichis adapted to drive a pair of gas cylinders. Accordingly, an additionalgas cylinder and piston arrangement may be connected to the left-handend of the piston 9, therein shown as by means of a connecting rod 15,only a portion of which is shown. In addition, the cap assembly 11includes a supply line 16 which is connected to the hydraulic cylinderat a successive compression stage whereby a plurality of compressionstages may be operated from an initial or single source of hydraulicfluid.

In order to seal the piston 4 within the gas cylinder 1 so that leakageof gas around the piston 4 is minimized, the circumference of the piston4 includes an annular seat 17 for receiving a piston ring assembly. Suchassembly is shown in detail in FIGURE 2, and includes any number ofcarbon-metal, or the like, hearing rings 18. Adjacent the bearing ringor rings 18 are a series of brass, or the like, sealing rings 19-23,each of which is L-shaped in cross section. Nested in said L-shapedrings 19-23 there are supported spring steel expander rings 24-28normally biasing specially constructed piston rings 29-33 radiallyoutwardly against the cylinder wall.

The construction of a preferred expander ring is shown in FIGURE 3, inwhich the same is tapered towards its opposed ends to equalize theexpansion stress. Each of the specially constructed piston rings 29-33comprises a continuous ring of tetrafluoroethylene resin (Teflon) or itslike, impregnated with glass fibers, or their like. This resin isremarkably well adapted to provide an effective seal under theencountered temperatures with the inner surfaces of the gas cylinder soas to prevent the flow of gas past the piston.

Due to the fact that, unreinforced, the resin is subject to excessivewear in use, it is necessary to incorporate therein a selected quantityof glass fibers. And the combination thereof has been found to resistwear and fortify the resin without diminishing the extraordinarygas-sealing characteristics of the resultant piston ring. Thus, it hasbeen found that an amount of glass fibers equal to approximately 25% ofthe piston ring by volume increases the useful life of the ringsapproximately five-hundredfold. Even greater amounts of glass fibers canalso be used to advantage, as will appear.

In order to minimize the flow of gases around and under the L-shapedrings 19-23, the seals 34-39 are included, and since these seals are notsubject to wear,

.they may compromise substantially pure tetrafluoroethylene, or itslike.

Because the piston rings 29-33 engage and wear against the inner wall, ahard layer on the inner surface of the cylinder is needed. Such isadvantageously formed by a plating of chromium having an appropriatethickness, e.g., approximately .003 inch, which is treated for requiredhardness and strength.

The fiberglass filler for the Teflon piston rings tend to be abrasive,and cut into or polish the cylinder wall against which they move. Thisabrasive polishing quality, which would normally be impractical incylinder walls of ordinary ferrous construction, is used to advantage bymeans of the hardened surface coating provided by the preferred chromiumplate on the inner surface of the subject cylinder wall. Thereby, theabrasive polishing action provides a smooth and accurate surface againstwhich the glass-filled Teflon forms a virtually perfect seal.

The L-shaped rings 19-23, the expander rings 24-28, and the piston rings29-33 are held in place on the piston 4 by means of any number of secondbearing rings 41, which are similar to the above-mentioned bearing ring18. A retainer ring 95 is threaded into the piston 4 to lock the pistonrings 29-33 and associated parts in place.

desired split-ring leakage in piston rings of conventional The Teflonrings are unbroken so as to avoid the un- 'rods 48 and 49.

construction. The use of the retainer ring structure permits thereplaceable insertion of the unbroken Teflon annuli as and for pistonrings, because the L-shaped brass retainer rings and the springyexpander rings retained therein are all individually and collectivelyremovable and replaceable. A silicone or other seal is included betweenthe gas cylinder 1 and the cylinder head 3 to eliminate any seepage ofgas which might otherwise occur past the cylinder head 3.

Said cylinder head 3 includes an intake check valve 97, which opens toallow gas to enter the cylinder 1 as the piston 4 travels to the left,and an outlet check valve 98, through which the gas passes from the gascylinder 1 when the piston 4 travels to the right, and vice versa in theopposed piston and cylinder on the corresponding left side of theapparatus.

In operation, hydraulic fluid, under pressure, is introduced into theconduit 12 which pushes the hydraulic piston 9. the left along with anyother pistons in successive stages which are similarly connected bymeans of conduit 16. As the hydraulic piston travels to the left the gaspiston 4 follows, the valve 97 opens, and gas is taken into the cylinder1 between the piston 4 and the cylinder head 3. At a predeterminedpressure point in the cycle, the hydraulic fluid is shut off from theconduit 12 and introduced to the opposite side of the piston 9 through aconduit (not shown) which may be similar to the conduit of the capassembly 11. The introduction of hydraulic fluid under pressure on theleft-hand side of the piston 9 causes the piston 4 to travel to theright in a compression stroke in which the gas passes from the cylinder1 through the valve 98.

In a particular embodiment, another gas cylinder and piston arrangementmay be connected to the left-hand end of the hydraulic piston 4 via theconnecting rod 15. Of course, the cycle of operation in the gas cylinderand piston connected to the left-hand end of the hydraulic piston 9 willbe opposite with respect to the gas cylinder 1 and piston 4. That is, asthe piston 4 advances to the left for a gas intake stroke, the left-handpiston will be advancing to the left for a compression stroke and whilethe gas piston 4 is advancing to the right on a compression'stroke, theleft-hand gas piston will be traveling in a gas intake stroke.

In FIGURE 4 there is illustrated a multiple stage gas compressorincluding three compression stages, each of which is preferablyconstructed in a manner similar to the new and improved piston andcylinder assembly shown in FIGURES l-3. Thus, the multiple stagecompressor of FIGURE 4 includes a first stage having a lefthand gascylinder 42, a right-hand gas cylinder 43, and an hydraulic cylinder 44.A gas piston 45, and a gas piston 46 in the gas cylinders 42 and 43 areeach connected to an hydraulic piston 47 by means of the piston In asimilar fashion, the second stage includes the gas cylinders 50 and 51,an hydraulic cylinder 52, the pistons 53, 54 and 55, and the connectingrods 56 and 57. Likewise, the third stage includes the gas cylinders 58and 59, the hydraulic cylinder 60, the pistons 61, 62 and 63, and theconnecting rods 64 and 65.

In operation, referring particularly to the apparatus of FIGURE 4, thehydraulic cylinder pistons 47, 5S and 63 are adapted to be moved backand forth by alternately connecting a source of hydraulic fluid underpressure to opposite sides of the hydraulic pistons. One suitable methodfor supplying hydraulic fluid under pressure is shown in which a dieselengine 66 drives a pump 67.

'on the drawing diagrammatically illustrate the path of hydraulic fluidflow therethrough in one of the respective positions of the same. Thus,when the valve is in one position, the hydraulic supply conduit 70 isconnected to a left-hand hydraulic cylinder supply line 72, and aright-hand hydraulic cylinder supply line 73 is connected to a returnconduit 74 which discharges into the reservoir 68. In another positionof the valve 71, the supply lines 72 and 73 are cross-coupled to theconduits 70 and 74, so that fluid is passed from the supply conduit 70to the right-hand supply line 73, while the left-hand supply line 72 isconnected to the discharge conduit 74 for releasing fluid into thereservoir 68. By switching the valve from one position to the other, thehydraulic pistons 47, 55 and 63 are correspondingly urged first in oneand then in the opposite direction, and thereby also the gas cylinderpistons 45, 46, 53, 54, 61 and 62 are reciprocated.

A gas to be compressed, or to be further compressed, such as helium, isintroduced to the multiple stage compressor of FIGURE 4 via an inletvalve 75, which is connected via the check valves 76 and 77 to the firststage gas cylinders 42 and 43. As the pistons 45, 47 and 46 inovetowards the left, the check valve 77 opens to allow gas to enter theright-hand gas cylinder 43, while the check valve 76 remains closed. Onthe other hand, when the pistons 45, 46 and 47 move to the right, thecheck valve 76 opens to allow gas to enter the left-hand gas cylinder 42while the check valve 77 remains closed.

As indicated in FIGURE 4, successive stages of the compressor includegas cylinders of smaller diameter, as desired, and in accordance withsound engineering requirements. By connecting the gas cylinders 42 and43 of the first stage to the gas cylinders of the second stage, the gasis expelled from the first stage into the smaller gas cylinder chambersof the second stage, thereby effecting a compression of the gas. Forthis purpose the gas cylinders 42 and 43 of the first stage areconnected via the check valves 78 and 79 to the intake check valves 80and 81 of the second stage gas cylinders 50 and 51. In a similar mannerthe outlet check valves 82 and '83 of the second stage gas cylinders 50and 51 are connected to the inlet check valves 84 and '85 of the thirdstage gas cylinders 58 and '59.

In operation, as the pistons move to the right, gas is forced into theleft-hand gas cylinders 42, 50 and 58 from the inlet valve 75 inthe caseof the first stage, and from the preceding stage in the case of thesecond and third stages. When the pistons move to the left, gas is takeninto the gas cylinders 43, 51 and 59 in the case of the first stage fromthe inlet valve 75 and the case of the second and third stages from thepreceding stage. The third stage gas cylinders 58' and 59 are connectedto the outlet line 86 via the check valves 87 and 88. Suitable safetyvalves and the like devices can obviously be added, as well as coolingapparatus within the skill of the art for securing against excesspressures and conveying away the heat of compression of the gases.

By virtue of a new and improved control system, the multiple stagecompressor of FIGURE 4 is adapted to handle the compression of gasesover a wide range of inlet pressures while at the same time operatingwith a high efiiciency. It will be appreciated that the length of thestroke of each of the pistons depends upon the pressure of the gasagainst which the piston is working, and the capacity of the pump 67 todeliver hydraulic fluid at a high enough pressure to move the pistonagainst the pressure of the gas. Of course, as the piston moves, thepressure of the gas increases due to the compression of gas resultingfrom the transfer of the gas into successively smaller chambers. Thus,when the inlet pressure of the gas is relatively low, it may be expectedthat the pump 67 will be capable of forcing hydraulic fluid into thehydraulic cylinders 44, 52 and 60, to cause the pistons to travelthrough a relatively long stroke. However, where the inlet pressure isrelatively high, the stroke is automatically shortened as needed tocorrespond to the 6 capacity of the pump 67 to deliver hydraulic fluidunder pressure and to insure that the maximum efiiciency of the pumpwill be realized.

It has been found that the pressure of the hydraulic fluid is theoptimum measurement of the efiiciency of operation of the pump.Accordingly, there is provided in the. multiple stage pump of FIGURE 4 apressure sensitive switch 89 connected to the left-hand hydrauliccylinder supply line 72, and another pressure sensitive switch 90connected to the right-hand hydraulic cylinder supply line 73. Thesepressure switches 89 and 90 are pre-set and adapted to sense thecondition where the fluid in the hydraulic cylinders approaches apredetermined level. Whenever the hydraulic pressure reaches suchpredetermined level, an appropriate one of the switches 89 and 90 isactuated. By linking the pressure switches 89 and 90 to the valve 71,the valve 71 is actuated to reverse the flow of hydraulic fluid into thehydraulic cylinders 42, 54 and 60, so that the travel of the pistons isreversed. The pressure sensitive switches 89' and 90 may behydraulically or mechanically linked to the valve 71, or as in theembodiment of FIGURE 4, a pair of solenoids 91 and 92 may beelectrically energized by the pressure switches 89 and 90 to switch thevalve 71. By means of the control system described above, the overalloperation of the compressor is controlled as a function of the hydraulicpressure so that maximum efl'lciency is achieved beyond any prior artapparatus.

An additional feature of the multiple stage compressor of FIGURE 4 isthe connection of the hydraulic cylinders 44, 52 and 60 in parallel sothat hydraulic fluid is supplied to each of the hydraulic cylinders froma single source. Due to the common connection of the supply lines 72 and73, the hydraulic pressure in each of the hydraulic cylinder 42, 54 and60 is inherently equalized, and since the hydraulic pistons 47, 55 and63 are not mechanically linked together, the length of the stroke ineach stage of the compressor automatically adjusts itself to the mostefficient mode of operation in accordance with the pressure of the gasbeing compressed in each individual compressor stage and the capacity ofthe hydraulic fluid pump 67 to deliver hydraulic fluid under pressure.

a This invention features the provision of new and improved piston ringconstruction either alone or in association with new and improvedexpander rings, retainer rings, and hardened complementary cylinderwalls. It also features a new and improved unbroken piston annulus ofnovel and valuable properties in combination with the described,preferred structure, or its like. In addition, the invention featuresthe provision of a multistage compressor structure having new andimproved hydraulically actuated and pressure-controlled operation toovercome the erratic and inefficient low-inlet pressure capacity ofprior art compressors. Moreover, the instant apparatus, by itspressure-controlled switching operation, assures the necessary pistondisplacement in the first compression stages, giving optimum efficiencyand rated capacity, irrespective of inlet or outlet pressures for theapparatus. Among other features is the provision of a constructionpromoting full use of all compression stages for a subject gas withinthe limits of available power.

While I have herein shown and described what I believe to be thepreferred embodiment of this invention,

. it is understood that modifications may be made in the combination,subcom-bination and methods thereof within the skill of the art and inthe light of the instant disclosure without departing from the spirit ofthe invention within the scope of the claims.

I claim:

1. In a gas compressor the combination of a plurality of pump stages,each of which includes a pair of gas cylinders and pistons, and a fluidoperated driving cylinder and piston, and piston rods connecting the gascylinder pistons and the driving cylinder pistons; a source of drivingfluid under pressure; means connecting the source of driving fluid tothe driving cylinders of each of the stages in parallel; valve means forselectively applying driving fluid to opposite sides of each of thedriving cylinder pistons to cause reciprocating motion of the drivingcylinder pistons within the driving cylinders; valve means to admit gasto the first stage gas cylinders; and means interconnecting gascylinders on one side of the driving cylinders to gas cylinders of asucceeding stage on the opposite side of the driving cylinders toprovide a progressive flow through successive stages thereof.

2. In a gas compressor, the combination of a plurality of pump stages,each of which includes a pair of gas cylinders and pistons, a hydrauliccylinder and piston, and piston rods connectingthe gas cylinder pistonsand the hydraulic cylinder pistons; a source of hydraulic fluid underpressure; means connecting the source of hydraulic fluid to thehydraulic cylinders of each of the stages in parallel; valve means forselectively applying hydraulic fluid to opposite sides of each of thehydraulic cylinder pistons to cause reciprocating motion of thehydraulic pistons within the hydraulic cylinders; valve means to admitgas to first stage gas cylinders and means interconnecting the gascylinders to provide a progressive flow through successive stagesthereof, the gas cylinders of each pump stage being on opposite sides oftheir respective hydraulic cylinders and gas cylinders being connectedto discharge into gas cylinders of a succeeding stage which are on theopposite side of the hydraulic cylinder of the succeeding stage. I

3. In a gas compressor the combination of a plurality of pump stages,each of which includes a pair of gas cylinders and pistons, a hydrauliccylinder and piston, and

piston rods connecting the gas cylinder pistons and the hydrauliccylinder piston; a source of hydraulic fluid under pressure; meansconnecting the source of hydraulic fluid to the hydraulic cylinders ofeach of the stages in parallel; valve means for selectively applyinghydraulic fluid to opposite sides of each of the hydraulic cylinderpistons to cause reciprocating motion of the hydraulic pistons withinthe hydraulic cylinders; means interconnecting the gas cylinders of eachof said stages for compressing gases as the hydraulic cylinder pistonsare reciprocated, and a pressure sensing device connected to thehydraulic cylinders and the valve means for actuating the valve means toreverse the travel of the hydraulic cylinder pistons whenever the fluidwithin the hydraulic cylinders achieves a predetermined pressure.

4. In a gas compressor, the combination of a plurality of stages; eachof said stages including a pair of gas cylinders and cooperatingpistons, an intermediate hydraulic cylinder and piston, and a piston rodconnecting the gas pistons and hydraulic piston whereby the pistonstravel together in unison; said gas cylinders being oppositely disposedabout the hydraulic cylinders so that in each stage the gas piston ofone gas cylinder moves in a compression stroke while the gas piston inthe other gas cylinder moves in an intake stroke; means connecting thegas cylinders of each stage to the gas cylinders of a successive stageso that gas may be transferred trorn each gas cylinder during acompression stroke to a gas cylinder of a succeeding stage during anintake stroke; a source of hydraulic fluid under pressure; a firsthydraulic fluid supply line connected to the hydraulic cylinders to eachof the stages on one side of each of the hydraulic pistons; a secondhydraulic fluid supply line connected to the hydraulic cylinders of eachof the stages on the other side of the pistons; 'a valve connected tothe first and second hydraulic fluid supply lines and the source ofhydraulic fluid under pressure; said valve being adapted to alternatelypass hydraulic fluid to the first and second fluid supply lines wherebythe hydraulic pis tons are reciprocated in the hydraulic cylinders; anda pressure sensing device linked to the hydraulic cylinder supply linesfor sensing a condition when the pressure within the hydraulic cylindersrises to a predetermined level; and means linked between the pressuresensing device and the valve for actuating the valve to change the flowof hydraulic fluid from one of the hydraulic fluid supply lines to theother of the hydraulic fluid supply lines whereby the direction oftravel of the hydraulic piston is reversed whenever the pressure of thehydraulic fluid rises to said predetermined level.

References Cited in the file of this patent UNITED STATES PATENTS261,605 Hill July 25, 1882 1,081,784 Spohrer Dec. 16, 1913 2,311,240Marien et a1. Feb. 16, 1943 2,315,798 Koether Apr. 6, 1943 2,437,341Aikman Mar. 9, 1948 2,791,370 Schemmel May 7, 1957 2,819,835 NewhallJan. 14, 1958 2,826,149 Wrigley Mar. 11, 1958 FOREIGN PATENTS 4,673Australia Oct. 20, 1932

